You raised the question about species senescence, but for some reason your
post disappeared into hyperspace and I no longer have it in my archives. Let
me address what I think your question is. And in so doing perhaps I will
address some of the issues and questions that others have posted.

(Incidentally can someone tell my why my postings are so often transmitted in
duplicate, and why responses to them are also in duplicate?)

I am interested in the process of aging not only in its individual
manifestation, but also in what I believe is its phyletic appearance as well.
We should not be surprised if we find that phyletic groups go through the
process of aging. Aging is ubiquitous, (but not universal) in nature. A few
organisms are immune from it, e.g., cancer cells, some trees, and some early,
simple organisms. The earliest and simplest organisms to appear seem to be
more immune from the process than are later, more morphologically complex
ones. In general, however, the process of aging is a pervasive feature of
the organic world.

What is it that becomes senescent in phyletic groups? I believe it is the
phyletic germ line. The germ line is what is continuous from generation to
generation in a phyletic group. What reason have we to believe that the germ
line is not subject to the process of aging? It accumulates detrimental
mutations, it loses its ability to correct errors, genes become
dysfunctional, all of which accumulate and are passed on to future
generations. The aging germ line produces individual organisms in the
phyletic group which, which show the characteristics associated with aging.
Some of these appear in the fossil record.

It should be noted that there is no satisfactory, widely accepted definition
of aging. All we can do is refer to its characteristics. What are they? At
the individual level they are as follows: decrease in size, especially in
linear, skeletal dimensions rather than mass; loss of morphological
structures; decrease in strength, robustness, speed, coordination;
decreasing mobility, geographic range, retreat to less demanding
environments; decreasing functionality of all systems; decline in population
size and density; increasing incidence of degenerative diseases, such as
those of the skeleton; increasing incidence of tumors and malignancies;
increasing incidence of infectious diseases; increasing vulnerability to
environmental trauma, such as accidents. These may be summed up in two
words, increasing decline and disorder. I think we can all visualize these
characteristics in ourselves as we grow older,
and in others.

Unlike the process of development and growth, the process of aging is less
"determined". One aging individual may display one suite of characteristics,
another individual may show a rather different suite. Yet both are aging
individuals.

The virtue of this list of characteristics of individual aging is that it is
independent of biological processes in groups of animals, i.e., species, and
thus avoids the problem of circularity. Thus these characteristics can be
applied not only to data from the fossil record, but in some cases to extant
groups of animals.

That is what I have done. With this list of characteristics in hand, I made
an unsystematic_search of paleontological and biological literature, looking
for studies of groups of animals that show one or preferably more of these
characteristics. Since most such studies are conducted in the evolutionary
framework, the data were often incomplete for what I wanted. Moreover, I am
an amateur at this game, and do not have at my fingertips a well stocked
research library. In brief, what I found is as follows:

I have identified 19 extant animal groups that are smaller than their
Pleistocene relatives which I interpret as evidence of aging in modern
species. Peters, D., 1986. Giants of Land, Sea & Air, Past & Present.
Sierra Club, San Francisco. National Geographic Society. 1983. Giants from
the Past. Washington, DC.

Granted that many of these studies are rather old, it must be born in mind
that the study of phyletic aging is pretty much taboo in the evolutionary
community, and no current biologist or paleontologist is likely to waste his
or her time on such problems.

I have completed a booklength MS on the topic of phyletic development, which,
of course, includes phyletic aging, and submitted a publishing proposal of it
to every university, commercial and religious publisher in the country that I
could locate. To no avail.